Researchers found that early accumulation of tau proteins in the brain as measured by PET scanner was more effective at predicting memory impairment than biomarkers in the cerebrospinal fluid or amyloid plaque in the brain.
From: Karolinska Institutet [in Sweden]
September
30, 2021 -- Over 50 million people around the world suffer from dementia.
Alzheimer's disease is the most common form of dementia and is characterised by
an accumulation of the proteins beta-amyloid (Ab) and tau in the brain,
followed by a continuous progression in memory decline. The pathological
progression can take different forms and it is difficult to predict how quickly
the symptoms will develop in any particular individual. Moreover, the presence
of Ab in a person's brain -- known as amyloid plaque -- does not necessarily
mean that the he or she will develop Alzheimer's dementia.
"There's been a rapid development
of different Alzheimer's biomarkers in recent years, enabling us to measure and
detect early signs of the disease in patients," says the study's first author
Marco Bucci, researcher at the Center for Alzheimer Research, part of the
Department of Neurobiology, Care Sciences and Society, Karolinska Institutet.
"But we still need to find tests that can predict the development of the
disease with greater specificity, so that we can improve not only its diagnosis
but also its prognosis and treatment."
Some biomarkers identify accumulations
of A? or tau, while others are used to measure the loss of nerve function
(neurodegeneration). Protein accumulation and neurodegeneration can be measured
in the cerebrospinal fluid (CSF) and plasma, or through brain imaging using
positron emission tomography (PET) and magnetic resonance imaging (MRI).
Current guidelines for the early detection of Alzheimer's disease with biomarkers
endorse the interchangeability of brain imaging methods and analyses of CSF
biomarkers (pTau and Ab), but this has been mooted. There is also a lack of
longitudinal studies showing how the biomarkers are linked to gradual cognitive
impairment.
"Our study shows that the presence
of amyloid plaque in the brain and changes in concentrations of Ab and pTau in
the CSF can be detected early during the course of the disease, but they do not
seem to have any correlation with later memory loss," says Dr Bucci.
"However, our results show that the presence of tau in the brain measured
by a PET scanner is linked to a rapid decline, especially of the episodic
memory, which is often affected at an early stage of the disease. Our
observation suggests that tau PET should be recommended for the clinical
prognostic assessment of cognitive decline in Alzheimer's patients."
The results are based on brain imaging
(PET and MRI) and CSF analyses in a group of 282 participants comprising people
with mild cognitive impairment, people with Alzheimer's dementia and healthy
controls. 213 of the participants were also monitored for three years with
tests of episodic memory (i.e. short term memory related to daily events).
"Our findings show that the
concentration of tau in the brain in Alzheimer's disease plays an important
part in its pathological progression and may become a key target for future
drug treatments," says principal investigator Agneta Nordberg, professor
at the Center for Alzheimer Research, Karolinska Institutet.
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